The recent global destruction of the environment is a matter of grave concern. In particular, nitrogen oxides (NOx) and sulfur oxides (SOx) released in air from burning fossil fuel such as coal and oil produce acid rain and acid fog which seriously destroy the environment of forests, lakes, marshes, etc. Above all, SOx are serious. SOx could be reduced in some degree by post-treatment, but it is important to efficiently remove sulfur from fuel oil. From the viewpoint of the protection of the environment, the regulation of gas oil in point of its sulfur content is much intensified, for which it is desired to develop a hydrogenation catalyst having a higher desulfurization activity.
Heretofore, a catalyst prepared from cobalt and molybdenum supported on a refractory inorganic oxide carrier such as alumina has been used for hydro-desulfurization of gas oil. It is known that the desulfurization activity of the catalyst significantly depends on the condition of the active metal, molybdenum therein. For improving the state of molybdenum on the catalyst, other carriers than alumina and alumina compounded oxide carriers have been investigated for the catalyst. Of these, it is known that a titania component improves the desulfurization activity of the catalyst. A method of applying titanium to an alumina carrier; and a method of co-precipitating alumina and titania are known.
Heretofore used are catalysts having an active metal of, for example, cobalt, nickel, molybdenum or tungsten supported on a refractory inorganic oxide carrier such as alumina. For improving the activity of the catalysts, methods of using an additional metal component, titanium have been proposed (Applied Catalysis, 63 (1990) 305-317; Japanese Patent Laid-Open No. 106061/1994). In these methods, however, the condition of titanium held in the carrier is not the most suitable, and the activity of the catalyst could not be improved satisfactorily.
For shaped articles of refractory inorganic oxides, heretofore known are extrusion moldings, spherical articles and honeycomb articles. In case where these shaped articles are used as carriers specifically for catalysts and adsorbents, generally employed is a method of applying thereto an active ingredient, an ingredient serving as a catalyst promoter to accelerate the activity or an ingredient for promoting adsorption, and a third ingredient for controlling the properties of the shaped article serving as a carrier.
In the system of the above where the reaction and adsorption to be occurred not only on the outer surface of the shaped article but also even inside the pores of the shaped article is an extremely important factor, the technique of uniformly introducing the ingredient participating in the reaction and adsorption into the deep inside of the shaped article is a matter of great importance.
However, to the case where the interaction between the ingredient and the shaped article serving as a carrier is extremely strong, a problem will occur that the ingredient is held only on the outer surface of the shaped article and could not uniformly penetrate into the pores existing inside the shaped article.
Concretely, the problem is as follows: When a metal compound to be carried by a refractory inorganic oxide carrier is applied to the carrier by impregnation method using the metal compound solution, and if the interaction between the metal compound and the carrier is strong, the carrier strongly adsorbs the metal compound or the metal compound is rapidly hydrolyzed on the carrier, and, as a result, the metal compound is held only on the outer surface of the shaped article, carrier and could not uniformly penetrate into the pores existing inside the shaped article.
Therefore, in the conventional method, the active ingredient is held only on the outer surface of the refractory inorganic oxide carrier, and could not effectively exhibit its ability expected for the intended reaction. In addition, another problem with the method is that the active ingredient, if segregated only on the outer surface of the shaped article, carrier, interferes with the diffusion of the reaction product into the pores inside the carrier.
For applying titanium to an alumina carrier, investigated are (1) a method of impregnation of alumina with an aqueous solution of titanium tetrachloride, (2) a method of impregnation of alumina with an isopropanol solution of titanium isopropoxide (Applied Catalysis, 63 (1990) 305-317), and (3) a method of chemical vapor deposition of a vapor of saturated titanium tetrachloride onto alumina under heat (Japanese Patent Laid-Open No. 106061/1994).
Both the method of applying titanium to an alumina carrier and the method of co-precipitating alumina and titania mentioned above include a step of applying an active metal of Group 6 and an active metal of Groups 8 to 10 of the Periodic Table to the carrier followed by calcining the metal-loading catalyst at a high temperature of around 500° C. or so, in which the active metals on the titania often agglomerate. This is problematic, as lowering the catalyst activity.
The method (2) requires the alcohol and is therefore uneconomical as the alcohol used must be recovered therein. The method (3) differs from ordinary impregnation methods where a solution is used. In this, a vapor of the starting material for the active ingredient is introduced into the reaction system, in which the vapor introduced is decomposed and deposited on the carrier having been controlled at a certain temperature. Therefore, this will require a complicated and troublesome apparatus for temperature control and process control. In addition, in this, chlorine deposits on the carrier and will produce hydrogen chloride gas when the refractory inorganic oxide carrier is processed at a high temperature in a reducing atmosphere, and the hydrogen chloride is troublesome as it corrodes the apparatus used.
On the other hand, the method of co-precipitating alumina and titania is uneconomical, since the titania could not sufficiently exhibit its effect if its amount is not large, for example, if smaller than 15% by weight.
In the methods (1) and (2), the active ingredient could not uniformly penetrate into the pores inside the shaped article of alumina, and therefore could not satisfactorily exhibit its effect. The method (3) differs from ordinary impregnation methods where a solution is used. In this, a vapor of the starting material for the active ingredient is introduced into the reaction system, in which the vapor introduced is decomposed and deposited on the carrier having been controlled at a certain temperature. Therefore, this will require a complicated and troublesome apparatus for temperature control and process control. In addition, in this, chlorine deposits on the carrier and will produce hydrogen chloride gas when the refractory inorganic oxide carrier is processed at a high temperature in a reducing atmosphere, and the hydrogen chloride is troublesome as it corrodes the apparatus used.
The present invention has been made in consideration of the above-mentioned matters, and its object is to provide a hydrogenation catalyst having higher desulfurization activity, denitrogenation activity and dearomatization activity, to provide a method of using the catalyst for hydrogenation of hydrocarbon oil, and to provide a metal compound-loading refractory inorganic oxide carrier in which the metal exists uniformly everywhere inside it.